So if air can be added and removed from a container, increasing or decreasing its overall mass, what happens if we keep the mass of the air the same and instead change its volume? What happens to the air?

With a syringe, students are modeling what's happening to the air as the system in which its contained when their finger blocked the end of it. Pushing and pulling on the plunger gave us some very interesting evidence for what air is capable of doing.

Students recognized that when they pushed the plunger in, the air was getting squished into a smaller space, or volume. This is called compression. When the plunger was pulled back, the same amount of air had a larger space, or volume. This is called expansion!